The co-production of propylene oxide and styrene monomer (the “POSM process”) involves the oxidation of ethyl benzene to form ethyl benzene hydroperoxide, the catalytic reaction of the hydroperoxide with propylene to form propylene oxide and 1-phenyl ethanol, and the dehydration of the 1-phenyl ethanol to produce styrene monomer. The basic patent describing this process is U.S. Pat. No. 3,351,635.
In the POSM process, various distillation steps are employed in order to separate unreacted reagents as well as various product streams, and generally one or more caustic treatment steps are employed in order to reduce the acidic characteristics of various streams. From the process, a heavy residue stream containing relatively high levels of sodium compounds is formed. Left untreated, the heavy residue is a low value product stream suitable only for use as a low grade fuel.
U.S. Pat. No. 5,210,354 discloses a process to upgrade the low value heavy residue and recover valuable products. The process involves treating the low value stream with aqueous acid, then phase separating the resulting mixture into an aqueous phase containing most of the sodium previously associated with the low value stream and an organic stream phase having reduced sodium content. The resulting organic stream phase can be directly cracked at elevated temperature with the formation of 1-phenyl ethanol and styrene or the organic stream phase can be passed to a wiped film evaporator where a volatile stream is separated and cracked to form 1-phenyl ethanol and styrene, the heavy stream from the evaporator comprising a useful fuel.
U.S. Pat. No. 5,276,235 discloses a process wherein the sodium-containing heavy residue formed in the POSM process is mixed with acid having a molar concentration with respect to water above that which corresponds to the product salt solubility limit. The resulting admixture is phase separated into an aqueous sodium salt-containing slurry phase and an organic phase having reduced sodium content.
In the prior art phase separation processes, it is found that large volumes of a rag layer tend to form in the separator vessels. The rag layer is an emulsion of water in the heavy organic layer that does not separate into either an organic or an aqueous phase. The rag layer prevents complete separation of the aqueous and organic phases, and reduces the efficiency of the separation process.
In sum, new and improved processes to upgrade the low value heavy residue produced in POSM process are needed.